It has previously been proposed to associate workpieces, or workpiece carriers, which are placed on a production line to characterize the specific workpieces or workpiece carriers so that workpieces, for example on the carriers, can be properly sorted, oriented, and assembly, or ejected because they are out-of-tolerance and the like. It has also been proposed to change the code which is associated with the respective workpiece or workpiece carrier to indicate the status of its machining or assembly, and/or to place a code on the workpiece or the workpiece carrier to indicate what type of machining or working is to be carried out, or what type of assembly, or assembly steps, is to be carried out at a further working station. The information carrier, typically, carries the code in form of a binary digital number, that is, coded in bit patterns. Reading stations are located along the production line which have stationary non-contacting sensors to sense or recognize the respective code carried by the code carrier.
One such known coding arrangement has a block in which coding bolts are located. The block is, preferably, secured to a workpiece carrier. Coding and decoding are carried out by shifting the bolts which can move between two terminal positions. The position of the bolts is sensed or interrogated by sensors responsive, for example, respectively, to a projected or retracted position of a bolt, or projected in one geometrical position and retracted in another. The sensors may be of various types, for example inductive sensors, light-responsive sensors responding to reflected light, for example light reflected from an end facing surface of the bolt, by light gates in which a light beam is interrupted, or not, depending on the position of the bolt and the like.
The number of coding bolts can be increased if a plurality of such coding bolts are located above each other, or adjacent each other, so that the information data which are encoded can be enhanced. For example, a predetermined operating or working station can have a device which engages one of the bolts to change the position of the bolt, for example to press the bolt inwardly, after the respective working step or process at the working station has been carried out. A reading or sensing station located in advance of the next subsequent working station then recognizes that the workpiece has been properly worked-on before, and the workpiece is, accordingly, handled in the next station. Upon non-recognition, the workpiece, for example on the carrier, can be shifted to an alternate or reject path.
A specific workpiece carrier can be recognized, hence, in flexible production lines, for example with flexible assembly belts or transport elements on which similar, adjacently located workpiece carriers are passed through the line. The corresponding coding on the workpiece carrier, upon recognition, then indicates to a sensing arrangement which work processes, or what kind of machine, or subassembly, has already been carried out, so that the particular workpiece carrier can be properly routed to the next station on which work is to be carried out on the workpiece.
It has been proposed--see the referenced German Patent Disclosure Document DE-OS No. 30 12 358, LEISNER and JUNG, assigned to the assignee of the present application--to locate coding bolts in pairs, the position of the bolts being sensed by inductive sensors. The coding bolts, always paired, are so coupled to each other that, if one coding bolt is depressed into an information carrier, the other coding bolt will be pressed outwardly of the information carrier. Such coding systems operate well, but require comparatively large space, so that workpiece carriers which are small cannot accomodate a plurality of such coding bolts. The room available for extensive information carriers is limited. The distances between the coding bolts must be sufficiently large to prevent errors or ambiguities both on coding as well as on reading the information. Entering data, and reading information on the information carrier, is possible, at times, only when the workpiece carrier is stationary. While this may be the case at some working stations, it interferes in some instances with orderly handling and transport of workpiece carriers, and workpieces themselves. The coding bolts, being moved mechanically, are subject to wear, particularly if the coding is changed frequently. Dust, dirt, moisture, oil mist and the like, are endemic to manufacturing processes, and accuracy of coding by the coding bolts may suffer in such environments.
It has been proposed to provide optically readable coding systems. Such systems are used, particularly in order to determine contents and the like of packaged goods. The coding system is especially suitable for distribution of packaged items. A certain coding field carries a plurality of respectively thick and thin lines which can be sensed by optical sensors. Such coding systems are suitable for controlled, clean environments--for example in supermarkets. Change of the information to be placed on the code carrier is not possible, so that such systems are not suitable for production lines where the code is to be changed, for example each time the workpiece passes a work station.
Magnetic coding systems for use with workpiece carriers have been proposed, in which a comparatively intense magnetic field is applied to an information carrier, for example a magnetizable sinter material, or a metallic surface. The information is then sensed and decoded by means of Hall sensors, or inductive sensors. To obtain unambiguous readings, the sensors must be located close to the information carriers. This may cause difficulties, particularly in production lines in which the workpiece carriers are not securely guided along a rigid track, but are subject to wobble, sway, and the like. Such systems permit change of the coded information by applying an intense a-c field, in order to erase the magnetic information, and then re-record new information on the information carrier.
The packing density of information on the information carrier is limited due to stray fields which are unavoidable in factory production lines, so that, if a substantial number of coded data are to be transferred between the code carrier and the sensor, space for reading and recording may not be available. In metal-working production lines there is always the danger that iron filings and the like will adhere to the magnetized portions of the information carrier, thus interfering with reading of stored information. Dust, dirt and other contaminants also impair the accuracy and transfer of data between the code carrier and sensors.